The degree to which observed natural climate variability is influenced by human emissions is unknowable, because we do not as yet understand all of the parameters of natural climate systems.
Furthermore, coupled ocean/atmospheric climate systems exhibit chaotic, nonlinear behavior, the results of which are unpredictable due to small differences in initial conditions, and highly variable limiting factors.
Even the IPCC has repeated a caution against using models as predictions of future climate states:
AR4 Climate Change 2007:
The Physical Science Basis
Glossary. p. 950
Since knowledge of the climate system’s past and current states is generally imperfect, as are the models that utilise this knowledge to produce a climate prediction, and since the climate system is inherently nonlinear and chaotic, predictability of the climate system is inherently limited. Even with arbitrarily accurate models and observations, there may still be limits to the predictability of such a nonlinear system.”
CLIMATE CHANGE 2001: THE SCIENTIFIC BASIS
Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change
Chapter 14.2 The Climate System
188.8.131.52 Balancing the need for finer scales and the need for ensembles; page 773
“In climate research and modelling, we should recognise that we are dealing with a coupled non-linear chaotic system, and therefore that the long-term prediction of future climate states is not possible.”
This underscores the fact that the results of numerical climate models are not predictions, but are hypotheses requiring validation through subsequent observations.
Therefore, the wild, hyperbolic headlines in popular press, websites, political statements and corporate publications are baseless wastes of electrons and dead trees.
Since climate models and the IPCC can’t tell us what will happen, even in the near future, let alone a hundred years to come, our only rational response to observed climate variability is to strive toward resilience and adaptability in our physical infrastructure, our governments, economics and cultural norms. We mustn’t put all of our climate response eggs in the basket of Anthropogenic Climate Change, lest we wake up one fine morning to discover that we have invested all of our egg money in preparation for a future that has not come to pass.
As Aldo Leopold told us 70 years ago:
A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise.